It has previously been proposed to measure knee motion in all three planes, and a typical article disclosing such measurement is "An Electrogoniometric Study of Knee Motion in Normal Gait" by Donald B. Kettelkamp, M.D., et al., the Journal of Bone and Joint Surgery, Volume 52-A, No. 4, June 1970, pages 775 to 790.
In general, what the prior analyses show is that the human knee is a relatively complicated joint, and its motion is not limited to hinge-type action around a single transverse axis as might initially be expected of the knee joint. This front-to-back motion, which of course is the principal and major motion of the knee, is known as flexion-extension. Full extension of the knee is when the leg is stretched out and the knee joint locked; and full flexion of the knee occurs when the leg is bent so that the calf is firmly against the thigh. Studies of the knee show that in the course of normal walking, for example, the knee goes through two flexion-extension cycles during each complete walking step, with maximum extension occuring during the swing phase, and an additional extension occurring during the time when the foot is engaging the ground. In addition to the flexion-extension motion, the knee also bends toward and away from the centerline of the body. This inward or outward motion is known variously as abduction/adduction, or varus/valgus motion, with "abduction" and "varus" referring to outward movement of the knee, and "adduction" and " valgus" referring to inward movement of the knee. In the present specification, we will use the designation varus/valgus but some of the prior articles use the comparable terms abduction/adduction. In addition to the two types of rotation mentioned above, the knee also may rotate about the long axis of the leg. This rotation is referred to as internal/external rotation. In summary therefore, the three types of motion of the knee to which reference will be made in the present specification are (1) flexion/extension, (2) varus/valgus, referring to the inward or outward bending of the knee, and (3) internal/external rotation.
The apparatus which has been employed up to the present time has been relatively cumbersome and massive, and the measurements which have been obtained have been similarly somewhat qualitative and inconsistent.
Accordingly, objects of the present invention include the provision of a lighter weight three-axis goniometer which is capable of measurement of athletes performing rapid and extreme physical movements, and one which will provide accurate and reliable information under such arduous conditions.
Another object of the present invention in to provide for the diagnosis of knee injuries by comparing a pattern produced by one leg before injury with the pattern produced by that leg after injury or by comparing the pattern produced by one (healthy) leg with that produced by the other (injured) leg.
Still another object of the present invention is to determine the torque which is produced under successive different controlled test conditions, for the purpose of testing athletic equipment or environments, such as foot gear and playing surface qualitites, by way of specific examples.